JPS585014A - Single mixer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mixer used on a planar circuit such as a strip line or a microstrip line, in which low noise characteristics can be obtained over a wide range, especially in the microwave band, and the intermediate frequency signal frequency can be reduced to GHz or GHz. The present invention relates to a microwave integrated circuit (MIC) integrated single fist mixer that provides a method for shorting diode loading points in the case of nearby high voltages.

In conventional mixers using MIC, a circuit as shown in FIG. 1 has been used as a method of short-circuiting the diode loading point at an intermediate frequency signal frequency. In Fig. 1, a high frequency signal input from terminal 1 propagates through main line 2 and goes to mixer e.
applied to diode 3. On the other hand, the local oscillation signal input from the terminal 4 is coupled to the main line 2 at high frequency, passes through a local oscillation signal band-pass filter (local oscillation BPF) s that selectively passes only the local oscillation signal, and is passed through a mixer diode. 3 is applied. Reference numeral 6 denotes a low-pass filter which extracts an intermediate frequency signal, which is a frequency component of the difference between the high frequency signal and the local oscillation signal, and is composed of a high frequency signal, an open end stub, and a series inductance. 7 is an intermediate frequency signal shorting circuit for shorting the terminal B of the mixer diode 3 for the intermediate frequency signal;
This is a low-pass filter consisting of a wavelength λ (7,)-long line and an i-wavelength open-terminated stub with low characteristic impedance, the terminal end of which is short-circuited to ground. 8 is an intermediate frequency signal output terminal from which the intermediate frequency signal generated by the mixer diode 3 is taken out.

In such a conventional intermediate frequency signal short circuit 7 using a low-pass filter whose terminal end is short-circuited to ground, there was no problem when the intermediate frequency signal frequency was relatively low, but as the intermediate frequency signal frequency became higher, The impedance of the intermediate frequency signal short circuit 7 can no longer be ignored, and it is no longer considered a short circuit. At this time, the impedance of the intermediate frequency signal short circuit 7 exhibits the characteristics of an inductance circuit having a certain finite magnitude. Since this intermediate frequency signal short circuit 7 is connected in series with the mixer diode 3 when viewed from the output terminal 8, as the impedance of the intermediate frequency signal short circuit 7 increases, the matching bandwidth from the intermediate frequency signal side is limited. This ultimately limits the bandwidth of the mixer. At the same time, main line 2 is connected to terminal B of mixer diode 3.
is connected, when the impedance of the intermediate frequency signal short circuit 7 increases, the impedance when looking from the intermediate frequency signal output terminal 8 to the mixer diode a side increases depending on the state of the circuit connected to the input terminal 1 side of the main line 20. This has the drawback of degrading the performance of the mixer due to mismatching of output impedance in intermediate frequency signals.

In order to reduce the impedance of the intermediate frequency signal short circuit 7 in order to alleviate this drawback, the dimensions of the intermediate frequency signal short circuit 7 may be shortened, or the intermediate frequency signal short circuit 7 may be shortened in size.
One possible method is to widen the width of the strip line constituting the main line 2 to lower the characteristic impedance, but if the dimensions are shortened or the line width is widened, the intermediate frequency signal short circuit 7 will increase the line impedance of the main line 2. Disturbed shi,
There is a drawback that the problem of increasing propagation loss arises.

One of the objects of the present invention is to eliminate the drawbacks of the above-mentioned conventional example, and to provide a main line in series with the main line that exhibits a passing characteristic for high frequency signals, but has an open impedance for intermediate frequency signals. An intermediate frequency signal blocking circuit is provided at the i wavelength (1-) of the intermediate λif frequency signal from the mixer diode, and the loading point of the mixer diode is short-circuited at high frequency using the intermediate frequency signal using the main line. This ensures that the loading point of the mixer diode is short-circuited even when the intermediate frequency signal frequency is high.

FIG. 2 shows one embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers and will be explained. The high frequency signal input from terminal 1 propagates through main line 2 and passes through mixer diode 3.
is applied to The local oscillation signal inputted from the terminal 4 is coupled to the main line 2 at high frequency, passes through the local oscillation BPF 6 that selectively passes the local oscillation signal, and is applied to the oxidation diode 3. Reference numeral 6 denotes a low-pass filter, which is long enough to take out intermediate frequency signals and at the same time short-circuit terminal A of mixer diode 3 for high frequency signals and local oscillation signals. is composed of an open-terminated stub of one wavelength (λ) of a high-frequency signal or local oscillation signal and a series inductance. Reference numeral 8 denotes an intermediate frequency signal output terminal for taking out the intermediate frequency signal generated by the mixer diode 3. 9 is an intermediate frequency signal blocking circuit that exhibits a pass characteristic for high frequency signals but exhibits an open impedance for intermediate frequency signals; It is provided.

In the embodiment shown in FIG. 2, the intermediate frequency signal blocking circuit 9 has an open impedance with respect to the intermediate frequency signal, and the mixer
Since the distance from the diode 3 to the intermediate frequency signal blocking circuit 9 is selected to be the length of one wavelength of the intermediate frequency signal, the terminal B of the mixer diode 3 is short-circuited in terms of high frequency by the intermediate frequency signal.

Therefore, even if the intermediate frequency signal frequency is high, the diode loading point can be reliably short-circuited. Further, since the intermediate frequency signal blocking circuit 9 is provided in series with the main line 2, it is possible to eliminate the influence of the short circuit state of the diode loading point B from the circuit connected to the terminal 1 side.

FIG. 3 shows another embodiment of the present invention, and the same parts as in FIG. 2 are given the same numbers and will be described. A high frequency signal input from terminal 1 propagates through main line 2 and is applied to mixer diode 3. The local oscillation signal inputted from the terminal 4 is coupled to the main line 2 at high frequency, passes through the local oscillation BPFs that selectively passes the local oscillation signal, and is applied to the mixer diode 3.

Reference numeral 6 denotes a low-pass filter, whose length is designed to short-circuit terminal A of the mixer diode 3 at high frequencies for high-frequency signals and local oscillation signals while at the same time extracting intermediate frequency signals. It consists of an open-terminated stub of one wavelength (-2) of the signal or local oscillation signal and a series inductance. Reference numeral 8 denotes an intermediate frequency signal output terminal for taking out the intermediate frequency signal generated by the mixer diode 3. Reference numeral 9 denotes an intermediate frequency signal blocking circuit that exhibits a pass characteristic for high frequency signals but exhibits an open impedance for intermediate frequency signals. 10 is a low-pass filter whose terminal end is short-circuited to ground, and is parallel to the main line 2 near the intermediate frequency signal blocking circuit 9. The distance from the ground shorted end 11 of the low-pass filter 1o to the mixer diode 3 is selected to be i-wave λ1g of the intermediate frequency signal.

In the embodiment of FIG. 3, the distance from the mixer diode 3 to the ground shorting end 11 is selected to be the length of 100 wavelengths of the intermediate frequency signal, and the intermediate frequency signal blocking circuit 9 is an open impedance for the intermediate frequency signal. Therefore, the terminal B of the mixer diode 3 is short-circuited at high frequency by the intermediate frequency signal. Therefore, even if the intermediate frequency signal frequency is high, the diode loading point can be reliably short-circuited. Further, since the intermediate frequency signal blocking circuit 9 is provided in series with the main line 2, it is possible to eliminate the influence of the short circuit state of the diode loading point B from the circuit connected to the terminal 1 side. Furthermore, since the terminal end also serves as a feedback circuit for the bias current flowing to the ground short circuit 3, there is no need to form a separate feedback circuit for the bias current, and the configuration of the mixer circuit is simplified.

FIG. 4 shows a specific method of constructing the intermediate frequency signal blocking circuit 9 in the embodiment of the present invention.

Figure 4a shows a wavelength line coupled interdigital DC blocking circuit in which two open-ended strip lines λ are distributed distributed over the length of approximately i wavelength (1) of the high-frequency signal from the open end. Additionally, it has a simple configuration, small size, low insertion loss for high frequency signals, and exhibits bandpass filter characteristics over a wide band. However, the capacitance between the gears due to the coupling gap of two distributed-coupled open-ended strip lines is, for example, when the high-frequency signal frequency is 12 GH.
For 2, it is usually less than 0.1P, and the capacitance between gears is 0.
．． Even if it is 1PF, if the intermediate frequency signal frequency is IGHz, the impedance shown by the capacitance between the gears is approximately 1.6
It can be seen that the impedance is close to the open impedance. Figure 4 shows a band-pass filter using a half-wavelength strip line resonator. By selecting the length λ of the half-wavelength strip line to be one wavelength (-H) of the high-frequency signal, it is possible to Although it exhibits pass characteristics, since one end of the line is open to intermediate frequency signals, it operates as an intermediate frequency signal blocking circuit and exhibits open impedance.

Conventionally, balanced mixers using two or four mixer diodes, which are relatively easy to obtain low noise characteristics over a wide band, have been used as MIC mixers using planar circuits such as strip lines and microstrip lines. Alternatively, double balanced mixers were common.

FIG. 6 is an example of a balanced mixer using MIC. The high frequency signal and the local oscillation signal input from the high frequency signal input terminal 12 and the local oscillation signal input terminal 13 are divided in power by 93 dB to the 3 dB directional generator 14 and applied to the mixer diodes 16 and 16, respectively. Then, an intermediate frequency signal, which is a frequency component of the difference between the high frequency signal and the local oscillation signal, is extracted from the intermediate frequency signal output terminal 18 via the low pass filter 17. Both 19 and 20 are intermediate frequency signal shorting circuits, which are provided to short-circuit the mixer diode 16 and the diode loading point of 16 at the intermediate frequency signal frequency, and are composed of a low-pass filter whose terminal end is shorted to ground. ing.

Although this balanced mixer can relatively easily obtain broadband characteristics, it has the drawback of requiring two mixer diodes, which increases the manufacturing cost of the mixer.

A single mixer, which requires only one mixer diode, is commonly used in waveguide circuits, and FIG. 6 is a block diagram thereof. To explain the operation of the mixer shown in FIG. 6, a high frequency signal inputted from a high frequency signal input terminal 21 passes through a band pass filter (BPF) 22 that selectively passes only the high frequency signal, and is applied to a mixer diode 23. The local oscillation signal input from the local oscillation signal input terminal 24 is coupled to the main line 26 only at the local oscillation signal frequency, passes through a band pass filter (BjF) 2e that selectively passes only the local oscillation signal, and is sent to the mixer. applied to diode 2:3 and mixer diode 23
The intermediate frequency signal generated by is passed through a low pass filter (LPF).
The signal is taken out from the intermediate frequency signal output terminal 28 via 27.

FIG. 7 shows the characteristics of BPF 22 and BPF 26 and important frequency components in the mixer. The high frequency signal frequency is f
72 local oscillation oscillation station wave number is fl.

The intermediate frequency signal frequency is fi f. In addition to the intermediate frequency signal, the mixer also generates an image signal (having frequency components of 2f, -fr and expressed by a frequency of fm) and a sum signal (having frequency components of fr+fi and expressed by a frequency of f8). The handling of image signals and sum signal components is important, especially when handling image signals with BPF22.
Since suppressing the image signal f! leads to improving the performance of the mixer, the high frequency signal fr is passed through the BPF 22 as shown in the characteristic 1s29, and the image signal f! For n, a characteristic is required to sufficiently suppress the busyness, and characteristic line 3 is required for BPF26.
0, the local oscillation signal f2 is passed through to generate the high frequency signal fr and the image signal f. Characteristics are required to sufficiently suppress this.

There are various problems that must be solved in order to realize the mixer having the configuration shown in FIG. 6 using a planar circuit such as a strip line or a microstrip line, which is mainly due to the low Q value of the planar circuit. In order to realize a single mixer with a wide band, low noise, and a high intermediate frequency signal frequency in the GHz band using MIC at a low cost, the following conditions must be satisfied.

(1) To have a filter that has low insertion loss for high-frequency signals, high suppression of image signals, and satisfies these characteristics over a wide band.

(2) The bandpass filter for local oscillation signals has the characteristic of greatly suppressing high frequency signals and image signals.

(At the same time as suppressing the image signal, the image signal is reconverted to an intermediate frequency signal again to achieve a configuration with good noise characteristics.) The structure should have a structure that minimizes propagation loss of high-frequency signals.

(@ G is an intermediate frequency signal short circuit that shorts the diode loading point of the mixer fist diode in the intermediate frequency signal.
f (to be realized in the z band.

(6) The circuit configuration of the mixer is simple.

The present invention provides a low-cost MIC single mixer that satisfies the above conditions and has a simple configuration, low noise, and wideband characteristics.

FIG. 8 shows another embodiment of the present invention. The high frequency signal input from the high frequency signal input terminal 31 propagates through the main line 32 and is applied to the mixer diode 33. 34 is a filter that exhibits a pass characteristic for high-frequency signals but suppresses image signals, and is composed of three stages of open-ended stubs, and is located at a position where the impedance seen from terminal C of mixer diode 33 is short-circuited by the image signal. The distance between the filter 34 and the mixer diode 33 is as follows: '35 short-circuits the terminals of the mixer diode 33 for the high frequency signal 1 local oscillation signal and image signal, and The signal is passed through a low pass filter. 36 is an intermediate frequency signal output terminal for outputting the intermediate frequency signal generated by the mixer diode 33. Reference numeral 37 denotes an intermediate frequency signal matching circuit, which is configured such that the impedance viewed from the intermediate frequency signal output terminal 36 to the mixer diode 33 side satisfies matching conditions. In particular, the intermediate frequency signal matching circuit 37 includes a parallel inductance circuit 31, which also forms part of a feedback circuit for the bias current flowing through the mixer diode 33. 38 is an intermediate frequency signal blocking circuit that exhibits a pass characteristic for high frequency signals but exhibits an open impedance for intermediate frequency signals, and is an i-wavelength line coupling type in which two open-terminated strip lines are coupled in an open-circuit distribution. It is composed of an interdigital DC blocking circuit, and the distance of one wavelength ('if) of the intermediate frequency signal from the mixer diode 33 is 4.
4. It is located at a distance of 4. The local oscillation signal input from the local oscillation signal input terminal 39 is applied to the mixer fist diode 33 via the local oscillation BPF 40 configured with a half-wavelength strip line resonator. It is provided at a position where the impedance viewed from the coupling point E to the filter 349111 is open or close to open at the local oscillation signal frequency. 41 and 42 are high frequency signal matching circuits, and the high frequency signal input terminal 31
The high-frequency signal matching circuit 41 is provided so that the impedance seen from the high-frequency signal can be matched with the high-frequency signal.
is composed of an open-terminated stub, and the high-frequency signal matching circuit 42
consists of low impedance lines. 43 is a feedback circuit for the bias current flowing through the mixer diode 33, and is composed of a low-pass filter whose terminal end is short-circuited to ground.

In the embodiment shown in FIG. 8, a three-stage open-ended stub filter 34, which is simple in construction and small in size, is used as a filter that exhibits a pass characteristic for high-frequency signals and suppresses image signals. Since the impedance is placed in a position where the image signal is short-circuited,
The high frequency signal input from the high frequency signal input terminal 31 is propagated to the mixer diode 33 with little propagation loss, and in order to efficiently convert the image signal generated in the mixer diode 33 into an intermediate frequency signal again, a mixer with low conversion loss is used. At the same time, mixer characteristics with a large image suppression ratio can be obtained.

Also, for intermediate frequency signals, an intermediate frequency signal blocking circuit 38 exhibiting open impedance is provided at a distance of i wavelength of the intermediate frequency signal from the mixer diode 33, so that the diode loading point C of the mixer diode 33 is an intermediate frequency signal and is short-circuited at high frequency. Therefore, even if the intermediate frequency signal frequency is as high as GHz band, the diode loading point C
'fI: An intermediate frequency signal can be used to reliably short-circuit. Further, since the intermediate frequency signal blocking circuit 38 is provided in series with the main line 32, it is possible to eliminate the influence of the circuit at the diode loading point C.

Therefore, the matching band for intermediate frequency signals is rarely limited, and low-noise mixer characteristics can be obtained over a wide band in the GHz band and high intermediate frequency signal frequencies.

Further, the intermediate frequency signal generated by the mixer diode 33 is passed through the low-pass filter 36 and the parallel inductance circuit 3.
7 is sequentially passed through the intermediate frequency signal matching circuit 37 including the mixer diode 33, and a parallel inductance circuit 37' which also serves as a feedback circuit for the bias current flowing to the mixer diode 33 is used as the intermediate frequency signal matching circuit 37.
There is no need to form a new Asumi style feedback circuit, and the configuration of the filter 34 is simple and small, so
The mixer circuit configuration is made smaller and simpler. Furthermore, since only one mixer diode is used, the manufacturing cost of the mixer is reduced.

FIG. 9 shows an example of a method of constructing the filter 34 in the embodiment of FIG. Connected to the main line train. Length Xl of open end stubs 46-47, f12.
I! , 1 is selected to be around one wavelength (-) of the image λ0 signal so that the attenuation pole of the filter is within or near the band of the image signal, and 124
4 Select so that the relationship <11 is satisfied. Open end stub 4
Regarding the interval of 2 degrees between 6 and 47, the two wavelengths (2 λr) of the high frequency signal are longer, the 2 wavelengths (, % Jr) are shorter, and the filter 34 is also shorter under the condition of 12 λ1 <Lo.
p, 4. corresponding to the characteristics required for. This filter is determined in relation to x2, but the high frequency signal frequency f, is determined in relation to the image signal frequency f! It has been confirmed that it operates effectively as a filter for a single mixer when f is higher than n and >fm.

For example, on a dielectric substrate with a relative permittivity of 2.6, an open-terminated stub with a characteristic impedance of 60Ω is connected to the main line with a characteristic impedance of 60Ω in parallel to the parallel IJ, and
=6.4 Nishiki, 11=s,s ss, 412==
4. If the frequency range is 11.7 to 13.0 GHz, the VSWR will be 1.6 or less, and the frequency range of 8 to 10.5 GHz will be obtained. This mine high frequency signal frequency is 12GH
Z band, intermediate frequency signal frequency is 1 GHz band, image signal frequency is 9 GHz band, and is effective as a filter for a single mixer with a bandwidth of around IGHz. Both stop band width and pass band width are wide bands of 1 GHz or more. It is. Moreover, the filter shown in the embodiment of FIG. 9 has a simple structure and small size, so that the insertion loss for high frequency signals is low.

In the embodiment described above, the local oscillation signal is applied to the mixer diode through the local oscillation BPF which is high frequency coupled to the main line between the intermediate frequency signal blocking circuit and the mixer diode. However, the method described in the embodiments does not necessarily have to be used. For example, a local oscillation signal may be input from terminal 1 at the same time as the high frequency signal, or the local oscillation signal may be applied to the mixer diode via the local oscillation BPFi coupled to the low pass filter 6 or 35 in high frequency. Needless to say.

An intermediate frequency signal blocking circuit that exhibits a pass characteristic for frequency signals but an open impedance for intermediate frequency signals is provided, and the distance between this intermediate frequency signal blocking circuit and the mixer diode is set to one wavelength of the intermediate frequency signal. By selecting the length of , the loading point of the first mixer die is short-circuited at high frequency by an intermediate frequency signal. Therefore, even when the intermediate frequency signal frequency is high, the diode loading point can be reliably shorted. Furthermore, since the intermediate frequency signal blocking circuit is provided in series with the main line, it is possible to eliminate the influence of the short circuit state of the diode loading point from the circuit connected to the high frequency signal input terminal side. Therefore, the matching band for the intermediate frequency signal is rarely limited, and low-noise mixer characteristics can be obtained over a wide band at high intermediate frequency signal frequencies. Moreover, since it is a single mixer, the mixer
Only one diode is required, and the manufacturing cost of the mixer can be reduced.

[Brief explanation of the drawing]

FIG. 2 is a pattern diagram of a mixer circuit according to an embodiment of the present invention, FIG. 3 is a pattern diagram of a mixer circuit according to another embodiment of the present invention, and FIG. 4a. b is a pattern diagram of a specific configuration of the intermediate frequency signal blocking circuit in the embodiment of FIGS. 2 and 3, a is a one-wavelength line-coupled interdigital DC blocking circuit, and b is a band pattern diagram using a half-wavelength strip line resonator. A diagram showing a pass filter, Figure 6 is a pattern diagram of a conventional balanced mixer using MIC,
Figure 6 is a block diagram showing the configuration of a single mixer often used in waveguide circuits, Figure 7 is a diagram showing the main frequency components of the mixer and the characteristics of the BPF shown in Figure 6, and Figure 8 is a diagram showing the main frequency components of the mixer. FIG. S is a pattern diagram of a single mixer circuit according to yet another embodiment of the invention, and FIG. S is a pattern diagram of a filter with three stages of open-ended stubs used in the embodiment of FIG. 1...High frequency signal input terminal, 2-...Main line, 3...Mixer diode, 4...
...Local oscillation signal input terminal, 6... Local oscillation BPF
, 6...Low pass filter, 8...Intermediate frequency signal output terminal, 1o...Intermediate frequency signal blocking circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 Figure 4 = 2 □ 5111 Figure 6 Figure 7 0

Claims (7)

[Claims] (1) In a single mixer using a microwave integrated circuit whose basic configuration is a strip line or microstrip line, the high frequency signal input terminal and the mixer
One end of the diode is connected to a main line that transmits a high frequency signal to the mixer diode, and a local oscillation signal is applied to the mixer diode, and the other end of the mixer diode is connected to a main line that transmits a high frequency signal to the mixer diode. A low-pass filter for extracting an intermediate frequency signal which is a difference frequency component is connected to the main line at a distance of i wavelength of the intermediate frequency signal from the mixer diode and is open to the intermediate frequency signal. A single mixer characterized by being provided with an intermediate frequency signal blocking circuit that indicates impedance. (2) As an intermediate frequency signal blocking circuit, an i-wavelength line-coupled interdigital direct current formed by distributively coupling two open-ended strip lines over a length of about i wavelength of the high-frequency signal from the open end of the open-terminated strip line. 2. A single mixer according to claim 1, characterized in that the single mixer is constituted by a blocking circuit. (3) The impedance seen from the mixer fist diode is configured with multiple stages of open terminal stubs connected in parallel to the main line at the position where the impedance is short-circuited at the image signal frequency, and the impedance is short-circuited at the image signal frequency. 2. The single mixer according to claim 1, further comprising a filter having a pass band at a high frequency signal station wave number. (4) whether the filters are equally spaced on the main line;
Alternatively, the first strands with open ends each having lengths 114, 112, and 113 are connected in parallel with each other at approximately equal intervals of 20. a second stub and a third stub; Length of second and third stubs x4. X2゜bu. Select the length of one wavelength or two wavelengths of the image signal so that the attenuation pole is within the image signal frequency band or near the image signal frequency band.1. g2. J, <
i. Either satisfies the condition J22<J 3<2゜<2ft2, or n2<11=, Q3(fi
1°, β1'2' to satisfy the condition of 0x222
Claim 3 characterized in that the length of 3 is selected.
Single mixer as described in section. (5) The first line provided on the main line. The spacing between the second and third stubs. 5. The single mixer according to claim 4, wherein: is selected to be longer than other wavelengths of the high frequency signal and shorter than other wavelengths. (6) An intermediate frequency signal matching circuit is provided on the output side of the low-pass filter, and this intermediate frequency signal matching circuit is constituted by at least one parallel inductance whose terminal end is short-circuited to ground, and at least one of the parallel inductances is 2. The single fist mixer according to claim 1, wherein one of the mixer diodes is used as a feedback circuit for a bias current flowing through the mixer diode. (7) A single mixer using a microwave integrated circuit whose basic configuration is a strip line or microstrip line is connected to the high frequency signal input terminal and the mixer.
One end of the diode is connected to a main line that transmits a high frequency signal to the mixer diode, and a local oscillation signal is applied to the mixer diode, and the other end of the mixer diode is connected to a main line that transmits a high frequency signal to the mixer diode. A low-pass filter for extracting an intermediate frequency signal, which is a difference frequency component, is connected to the main line, and the intermediate frequency signal r is connected to the main line at a distance equal to the λ wavelength of the intermediate frequency signal from the mixer diode.
(For this purpose, an intermediate frequency signal blocking circuit exhibiting an open impedance is provided, and a low-pass filter terminated in parallel with the main line on the mixer diode side or short-circuited to ground is installed in the vicinity of this intermediate frequency signal blocking circuit. A single mixer, characterized in that the distance from the ground short-circuited end of the low-pass filter connected to the mixer diode, the end of which is short-circuited to ground, to the mixer diode is selected to be the length of one wavelength of the intermediate frequency signal.